Method of sealing and evacuating vacuum envelopes

ABSTRACT

THE TWO INSULATING CASINGS OF A VACUUM ENVELOPE ARE PLACED IN CLOSE PROXIMITY, AND A PLURALITY OF SPACED USHAPED BRAZING SHIMS ARE DISPOSED IN SPACED RELATION AROUND AN ANNULAR BRAZING SHIM, THE LATTER BEING POSITIONED BETWEEN THE CONFRONTING ENDS OF THE TWO CERAMIC, OR INSULATING RINGS CONSTITUTING THE ENVELOPE OF THE ENCLOSURE. THE ENVELOPE IS PLACED WITHIN A VACUUM FURNACE AND HEATED TO A TEMPERATURE JUST BELOW THE MELTING TEMPERTURE OF THE U-SHAPED BRAZING SHIMS. IN EFFECT, THIS CREATES A PERIPHERAL OPENING PERMITTING THEREBY A COMMINICATING PASSAGE BETWEEN THE INTERIOR AND THE EXTERIOR OF THE ENVELOPE FOR OUTGASSING PROCEDURES. WHEN THE DESIRED DEGREE OF OUTGASSING AND EVACUATION HAS OCCURRED, THE TEMPERATURE OF THE VACUUM FURNACE IS RAISED TO THE MELTING POINT OF THE PLURALITY OF SPACED BRAZING SHIMS, AND THEY MELT FLOWING INTO THE SPACE BETWEEN THE TWO CERAMIC OR INSULATING CASINGS, AND SEALING THE SAME TOGETHER. NO TUBULATION IS NEEDED WITH THIS METHOD.

Aug. 14, 1973 BEREZA Re. 27,733

METHOD OF SEALING AND EVACUATING VACUUM ENVELOPES Original Filed Sept.30, 1969 3 Sheets-Sheet 1 2 m 9 M F J mg \u \\\\m up B 0 H72 3 6INVENTOR Albert Berezo ATTORNEY FIG.|.

l fl w y M J 1 I F/ W w w s y M MW H A 6 F H V w 2 4 Aug. 14, 1973BEREZA Re. 27,733

METHOD OF SEALING AND EVACUATING VACUUM ENVELOPES Original Filed Sept.30, 1969 5 Sheets-Sheet 2 FIG.3.

A. BEREZA Re. 27,733

METHOD OF SEALING AND EVACUATING VACUUM ENVELOPES Aug. 14, 1973 3Sheets-Sheet 3 Original Filed Sept. 50, 1969 FIGS.

United States Patent 27,733 METHOD OF SEALING AND EVACUATING VACUUMENVELOPES Albert Bereza, Elmira, N.Y., assignor to Westinghouse ElectricCorporation, Pittsburgh, Pa.

Original No. 3,656,225, dated Apr. 18, 1972, Ser. No. 862,401, Sept. 30,1969. Application for reissue Oct. 13, 1972, Ser. No. 297,527

Int. Cl. B23k 31/02 U.S. Cl. 29472.7 8 Claims Matter enclosed in heavybrackets ['1 appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE The two insulating casings of a vacuumenvelope are placed in close proximity, and a plurality of spaced U-shaped brazing shims are disposed in spaced relation around an annularbrazing shim, the latter being positioned between the confronting endsof the two ceramic, or insulating rings constituting the envelope of theenclosure. The envelope is placed within a vacuum furnace and heated toa temperature just below the melting temperature of the U-shapcd brazingshims. In effect, this creates a peripheral opening permitting thereby acommunicating passage between the interior and the exterior of theenvelope for outgassing procedures.

When the desired degree of outgassing and evacuation has occurred, thetemperature of the vacuum furnace is raised to the melting point of theplurality of spaced brazing shims, and they melt flowing into the spacebetween the two ceramic or insulating casings, and sealing the sametogether. No tubulation is needed with this method.

CROSS-REFERENCES TO RELATED APPLICATIONS Applicant is not aware of anyrelated application pertinent to the present invention.

BACKGROUND OF THE INVENTION The present invention relates to the art ofoutgassing, evacuating, and sealing envelopes, which constitute vacuumtubes, vacuum-type circuit interrupters, and other vacuum devices. Apresently-used method for evacuating and sealing vacuum tubes and othervacuum envelopes involves an open tubulation connected to the tubeenvelope. At the proper time in the process of making the vacuum tube,after the gases in the tube enclosure have been exhausted through thetubulation, the tubulation is sealed off. A portion of the tubulationbetween the seal and the envelope projects from the tube envelope.Furthermore, this tubulation is a weak, or vulnerable part of the tubeenvelope. In many forms of vacuum tubes, and particularly in cathode-raytubes, the tubulation is positioned in the middle of the stern of thetubes within the circular array of base pins. In vacuum-type circuitinterrupters, the tubulation generally projects from one of the end capsof the device, and needs protection.

In the presently-used method of evacuating a cathoderay tube, involvinga tubulation, the tube is evacuated in an evacuation oven under propertemperature conditions for this purpose. It is inconvenient to seal thetubulation while the tube is in the oven: therefore, when the tube hasbeen evacuated, it is removed from the oven during the sealing-otfprocess. At that time, at least a portion of the tube envelope isexposed to lower-than-evacuation temperatures, resulting in concomitantchance of implosion, or cracking of the tube envelope, during thesealing-off operation.

In addition to the foregoing disadvantages, the presently-usedevacuation method requires provision of the tubulation, which involvessupplying material in addition to the material used in the tubeenvelope.

SUMMARY OF THE INVENTION The present invention is particularly concernedwith the evacuation and sealing-0E of vacuum envelopes while in thevacuum furnace. According to a preferred embodiment of the presentinvention, there is provided a plurality of spaced brazing shims, whichmay be manually wrapped around a portion of an annular ring-type brazingseal, and this provides a peripheral clearance between the twoconfronting edges of the ceramic casings. In other words, acommunicating passage is provided peripherally around the envelope, sothat ready egress of gases may occur, passing outwardly into the vacuumfurnace to be drawn off by the vacuum-creating equipment.

According to the preferred process of the present invention, theprovision of the spaced brazing shims provides such clearance, and thetemperature of the vacuum furnace is maintained just beiow thatnecessary to melt the brazing shims.

At the desired point in the outgassing and evacuation process, thetemperature of the vacuum furnace is raised quickly to a point above themelting point of the brazing shims, which action causes them to melt,and to flow between the conjointly disposed end faces of the ceramic, orinsulating casings. This provides, in one operation, a tight sealbetween the confronting ends of the insulating casings.

The temperature of the vacuum furnace may then be gradually reduced insteps to anneal the casing walls and gradually reduce the temperature ofthe component parts of ambient temperature.

It is, accordingly, a general object of the present invention to providemeans for a method of evacuating and sealing a vacuum device, orenvelope not having the disadvantages of the presently-used evacuatingand sealing operation involving a tubulation.

It is a further object of the present invention to provide a means for,and a method of evacuating and sealing, which results in an enclosurehaving a shorter overall length than the presently-used envelopes due tothe omission of the tubulation.

It is a further object of the present invention to facilitate evacuatingan enclosure by providing an evacuation path through the tube envelopehaving a larger diameter, and a shorter length than that possible usingthe tubulation method of evacuating and sealing.

It is a further object of the present invention to present less chancethan heretofore of implosion or cracking of the tube envelope whilesealing.

Further objects and advantages will readily become apparent upon readingthe following specification taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional viewtaken through a vacuum furnace, illustrating a vacuum-type circuitinterrupter being evacuated and sealed in accordance with the method ofthe present invention;

FIG. 2 is an enlarged fragmentary view of a portion of the jointexisting between the confronting ends of the two insulating casings ofthe device illustrated in FIG. 1, taken at the circle A" in FIG. 1;

FIG. 3 is a considerably-enlarged vertical sectional view taken throughthe vacuum-type circuit interrupter of FIG. 1, illustrating thecomponent parts interiorly thereof following the sealing operation;

FIG. 4 is a top plan view, taken substantially along the line IV-IV ofFIG. 3 illustrating the condenser shield and its support and eliminatingthe contact structure for clarity;

FIG. is a perspective view of one of the brazing shims used in thepresent invention; and

FIG. 6 is a perspective view of the positioning of one of the brazingshims encircling a portion of one of the annular brazing shims.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, andmore particularly to FIG. 1 thereof, the reference numeral 1 generallydesignates a vacuum furnace, as customarily utilized in the evacuationand sealing of vacuum-type devices, such as tubes, cathode-ray tubes,circuit-breaker envelopes, gas discharge tubes and the like. As wellknown by those skilled in the art. generally the vacuum furnace 1comprises an upstanding support 2 which supports an upper platform 3 andenclosure 4, the latter enclosing a space 5 which may be heated to anydesired temperature by resistance means, such as designated by thereference numeral 6, and being connected by suitable valve means 8 to avacuum pump 9.

The representation, as set forth in FIG. 1, is somewhat diagrammatic,inasmuch as the vacuum furnace 1 is well recognized and understood bythose skilled in the art.

Supported in an upstanding relationship upon a pair of spaced supportmembers 11 is a vacuum-type circuit interrupter device 13 clampedbetween a pair of metallic end plates 14, 15 by a plurality of clampingrods 16, each of which has clamping nuts 17 threaded thereto.Preferably, the clamping rods 16 are made of molybdenum, which has acoefficient of thermal expansion less than that of the two ceramicsleeves 19; 20 which generally constitute the evacuated envelope 21 ofthe vacuum-type circuit interrupter 13. FIG. 3 may be referred to inconnection with the general type of device 13 involved.

With reference to FIG. 3, it will be noted that a vacuum-type circuitinterrupter is generally designated by the reference numeral 13. Asshown in FIG. 3, the circuit interrupting device 13 generally comprisesa stationary contact 23 having a stationary stem portion 23a, which isbrazed to an upper end plate 25. Cooperable with the stationary contact23, and separable therefrom to establish an arc, is a lower movablecontact, generally designated by the reference numeral 27.

The movable contact 27 comprises a movable contact member, shown in theclosed-circuit position, and attached to a movable stem portion 27a, thelatter being sealed to the upper end of a sylphon metallic bellows 2.9.The lower end of the metallic bellows 29 is sealed within an opening 30provided through the lower end plate 31 of the device 13. As well knownby those skilled in the art, a suitable operating mechanism may bemechanically connected to the lower movable stern portion 27a to effectthe actuation of the circuit-interrupting device 13, when utilizedwithin operative equipment. The present invention, however, is notconcerned with the intricacies of operation of the vacuum-type circuitinterrupter 13, but specifically only with the sealing means forproviding the outgassing procedures, and effecting the desired degree ofevacuation with a final sealing operation, which constitutes the essenceof the present invention.

In the particular type of device 13, which is utilized as an example ofthe present invention, it will be observed that a condensing shield 32,usually made of copper, or stainless steel, for example is used tocondense metallic vapor during interruption. A plurality, such as threetabs 34a constitute an integral part of a flange ring 34, which ispreferably made of a nickel-iron alloy, and generally comprising roughly42 percent nickel and 58 percent iron; or the material could be Kovar,which is a trademark of the Westinghouse Electric Corporation andconsisting of -34 percent nickel, 4-l7 percent cobalt, less than 1percent manganese, and the balance iron. Consult U.S. Pat.

4 Nos. 2,217,422; 1,872,354; and 1,942,261. The flange ring 34 may bemade of a number of materials which match the expansion of the ceramiccylinders.

As illustrated in FIG. 3, it will be noted that generally, the envelope,generally designated by the reference numeral 21, comprises a pair ofspaced ceramic sleeves 19, 20 disposed in alignment, and having theirends 19a, 20a, disposed in confronting relationship. As a prioroperation, the confronting ends 19a, 20a, of the ceramic sleeves 19, 20are first metallized with a suitable molybdenum-manganese formulation,which may be painted on by a brush, or applied by a silk-screentechnique, as well known by those skilled in the art. Subsequent to theapplication of the moly-manganese formulation, the individual sleeves19, 20 are fired at a temperature say 1,540 C. for 178 hours. As a lateroperation, the ends of the ceramic sleeves 19, 20 are painted with agrade B pure nickel powder in a vehicle by either a brush operation, ora silk-screen technique and the subsequent nickel coating is fired as asecond firing operation for 800 for roughly 10 minutes and to l,000 C.for approximately 5 minutes. Following these preliminariy metallizingsteps, the ceramic sleeves 19, 20 are ready for the evacuation andsealing operation of the present invention.

The component parts of the vacuum-type circuit interrupter 13 are placedinto position, and a brazing ring or shim 37, made of a silver-coppereutectic alloy, sold under the trademark BT" by many suppliers, one ofwhich is the Handy and Harman Company located at 82 Fulton Street, NewYork City, is used between the ends 19a, 2021. This BT material,constituted by the aforesaid silver-copper eutectic alloy, flows atapproximately 778 C. This BT material is used not only for the brazingrings or shims 37 of the present invention, as described hereinafter,but also for the U-shaped shims or tabs 39 which are illustrated indetail in FIG. 5 of the drawings.

Returning to the assembly steps, a solder ring or shim 37 of theaforesaid BT material is placed against the metallized lower surface 19aof the upper ceramic sleeve 19. A plurality, such as three, or incertain instances a greater number, such as six, U-shuped brazing shimsor tabs 39 of the same BT material are wrapped around a portion 37a ofthe brazing rings 37, as illustrated in FIGS. 2 and 6, and placed intoposition against the lower end 19a of the upper ceramic sleeve 19.Immediately below the brazing ring 37 is the supporting flange portion34 of the condensing shield 3, which, as previously described, is madeof Kovar, or a nickel-iron material with the desired expansioncharacteristics. Then follows another brazing ring or shim 37, which isdisposed below the flange 34 and immediately against the upper endsurface 20a of the lower ceramic sleeve 20. See FIG. 2 in thisconnection.

Additional brazing rings 37 made of the same B'l"" material are disposedat the upper and lower metallized end surfaces 19b, 20b of the ceramicsleeves 19, 20 between the annular flanges 43, 44 of the end metallicplates 25, 31. The end metallic plates 25, 31 may, for example, bestainless steel, having Kovar" or nickel-iron flange rings 43, 44, orthe end plates 25, 31 may be made entirely of K-ovar or nickel-ironmaterial.

It will be observed that by utilizing a plurality of spaced brazingshims or tabs 39, there results a peripheral communcating passage 50(FIG. 4) which may, for example, be 8 mils thick to permit therebyegress of the occluded gases, and other gaseous by-products, which arebaked out of the metallic component parts of the vacuum-type circuitinterrupter 13.

The vacuum furnace 1 is raised to a temperature below that of the 778 C.value, at which the BT shims 39 and brazing rings or shims 37 wouldmelt, and at the temperature below this value 778 C. the outgassingprocedures and evacuation steps are employed, as well known by thoseskilled in the art.

It is obvious that in the operation of a vacuum-type circuit interrupter13, due to the heat of arcing, it is desirable to utilize as componentparts interiorly of the envelope 21 metallic parts, which the occludedgases and other gaseous by-products removed therefrom. Also a relativelyhigh vacuum, say 10- torr, is generally employed.

When the desired degree of evacuation and outgassing of the occludedgases has occurred, the temperature of the vacuum furnace 1 is quicklyraised to a value above the 778 C. flowing temperature of the brazingshims 37 and 39, say, for example, 850 C. maximum. These will then, ofcourse, flow together to provide a hermetic seal.

The differential expansion of the side rods 16 now act to compress theentire unit 13 to a closed position, and with the brazing alloycompletely flowed, the furnace 1 is shut off.

By way of recapitulation, the operation of the furnace 1 would be asfollows: There is a pre-pump down cycle for /z to A of an hour, toreduce the pressure to 10- torrs. The heat is then turned on the furnaceby energizing the resistance coils 6, and the furnace attains atemperature of 650 C. for 2% hours. Then occurs an outgassing step of 2hours to 3 hours at a temperature roughly 650 C. There then follows a 1hour bake-out at 725 C. It will be noted that all during the aforesaidtime, the temperature is below that of the melting point of the BT shims39 and brazing shims 37.

Following the aforesaid procedures, the vacuum furnace is conductedthrough a brazing cycle for 25 minutes at 850 C. Then the furnace isgradually allowed to cool down, the sealing having been completed by theaforesaid rise of temperature to the 850 C. value.

There results a 2% hour cool-down period for the parts to graduallyassume ambient, or normal room temperature.

Generally, it take 7 /2 hours for the entire aforesaid procedure beingconducted within the vacuum furnace 1.

From the aforesaid description, it will be apparent that no tubulationis required, and a free peripheral communicating passage 50 is providedbetween the two ceramic sleeves 19, 20 to permit the occluded gases tofreely pass radially outwardly, and to be drawn through the vacuum pump9 associated with the vacuum furnace 1.

Although the process of the present invention has been described withparticular rerationship to a vacuum-type circuit interrupter 13, it willbe obvious to those skilled in the art that the improved sealing methodof the present invention may be applied to other vacuum-type devices,such as vacuum tubes, discharge tubes, or related equipment, in whichbake-out operations and evacuation steps are desired.

Although there has been illustrated and described a specific process, itis to be clearly understood that the same was merely for the purpose ofillustration, and that changes and modifications may readily be madetherein by those skilled in the art, without departing from the spiritand scope of the invention.

I claim:

1. The method of evacuating and sealing an envelope comprising twoaxially-aligned ceramic sleeves, comprising the steps of:

(a) positioning a plurality of brazing shims at spaced points on abrazing ring;

(b) placing the aforesaid brazing ring with the assembled spaced brazingshims thereon between and in (d) performing usual outgassing andevacuation steps while maintaining the furnace temperature below themelting temperature of the spaced brazing shims;

(e) raising the furnace temperature to a temperature above the meltingtemperature of the brazing shims to cause flowing thereof into thebrazing ring to seal the two axially-aligned sleeves together;

(f) reducing the temperature of the furnace; and,

(g) removing the sealed evacuated device from the furnace.

2. The method of claim 1, wherein the shims and the brazing ring areformed of the same material.

3. The method of claim 2, wherein the material is a silver-coppereutectic alloy melting at approximately 778 4. The method of claim 1,wherein the brazing shims are of U-shape and wrapped spatially about thebrazing ring.

5. The method of evacuating and sealing an envelope comprising a ceramicsleeve and a metallic member, comprising the steps of:

(a) positioning a plurality of brazing shims at spaced points on abrazing ring;

(b) placing the aforesaid brazing ring with the assembled spaced brazingshims thereon between and in mating engagement with the confrontingsurfaces of the ceramic sleeve and said metallic member to provide aperipheral communicating passage to permit egress of gases duringevacuation;

(c) placing the entire device within a vacuum furnace:

(d) performing usual outgassing and evacuation steps while maintainingthe furnace temperature below the melting temperature of the spacedbrazing shims;

(e) raising the furnace temperature to a temperature above the meltingtemperature 0) the brazing shims to cause flowing thereof into thebrazing ring to seal the ceramic sleeve and the metallic membertogether;

(f) reducing the temperature of the furnace; and,

(g) removing the sealed evacuated device from the furnace.

6. The method of claim 5, wherein the shims and the brazing ring areformed of the same material.

7. The method of claim 6, wherein the material is a silver-coppereutectic alloy melting at approximately 778 C.

8. The method of claim 5, wherein the brazing shims are of U-shape andwrapped spatially about the brazing ring.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the oringinal patent.

UNITED STATES PATENTS 2,647,218 7/1953 Sorg et al 29-427.7 UX 2,650,6839/1953 McPhee et al. 287189.365 2,709,147 5/1955 Ziegler 29-472.7 X2,857,663 10/1958 Beggs 29-473.1 3,069,766 12/ 1962 Rush 29-501 X3,088,201 5/1963 Louden et a1 29-501 X 3,091,028 5/1963 Westbrook et al.29473.1 3,465,943 9/1969 Clark et al. 29-501 X 3,479,170 11/1969 Louden29-501 X 3,487,536 1/ 1970 Goldstein 29-501 X J. SPENCER OVERHOLSER,Primary Examiner R. J. SHORE, Assistant Examiner US. Cl. X.R.

